1. Technical Field
The invention relates to a resonator that excites a thickness-shear vibration mode, and more particularly, to a resonating element having a so-called inverted mesa structure, a resonator, an electronic device, and an electronic apparatus using the resonator, a moving vehicle using the resonator, and a method of manufacturing the vibrating element.
2. Related Art
An AT-cut quartz crystal resonator which is an example of a resonator is used in various fields such as in a piezoelectric oscillator and an electronic apparatus since it excites a thickness-shear vibration mode as its main vibration mode and is ideal for decreasing size and increasing output frequency, as well as exhibiting excellent cubic curve with frequency-temperature characteristics.
In recent years, there has been a demand to further increase the output frequency of the AT-cut quartz crystal resonator, which has led to a need to further decrease the thickness of a vibrating portion of a resonator element used in the AT-cut quartz crystal resonator. However, there is a problem in that when the vibrating portion is made thinner, the rigidity of the vibrating portion decreases, and the impact resistance or the like deteriorates.
To solve this problem, for example, JP-A-2003-264446 discloses an AT-cut resonator having a so-called inverted mesa structure which increases the output frequency by forming depressed portions (vibrating portions) on both principal surfaces, namely the front and rear surfaces of a quartz crystal substrate so as to face each other. Specifically, the AT-cut resonator has a configuration in which a third thick-walled portion is formed along an X-axis direction of the vibrating portion, and a first thick-walled portion and a second thick-walled portion are formed along the outer edges in a Z-axis direction of the vibrating portion with the vibrating portion interposed so as to extend from both end portions of the third thick-walled portion. An X-long substrate is used as the quartz crystal substrate, and an excitation electrode is formed in a region where the flatness of the vibrating portion formed in the depressed portion is secured.
However, since etching is generally used in forming of the AT-cut resonator having the inverted mesa structure, an etching residue (also referred to as “fillet”) is generated at the boundary between the vibrating portion and the first and second thick-walled portions formed along the Z-axis direction. However, it is confirmed that there is a problem in that when this etching residue is generated, the effective area of the vibrating portion decreases, and a CI value of a main vibration mode and the ratio (CIs/CIm) of a CI value (CIs) of an adjacent spurious vibration mode to the CI value (CIm) of a main vibration mode or the like does not satisfy a standard value (for example, 1.8 or more).